The program has as its broad aim an understanding of the biological foundation of language through the study of its structure and acquisition in a visual-gestural language. In the research under the renewal grant, the general focus is on the structured use of space and simultaneity in the grammar of sign language. The study includes a fine-grained analysis of the acquisition of American Sign Language, as a natural primary language, by young deaf children of deaf parents. We are proposing a series of studies which represent the first major excursion into a previously uncharted area -- the grammar of sign language. We will study in depth the structure and acquisition of the grammatical processes and mechanisms which are used by a language in a visual mode. The underlying regularities of sign language which we investigate from a structural and developmental point of view include: a) The grammatical processes that modulate meaning (analogous to infectional morphology of spoken languages) which are accomplished by simultaneous modification of the form of signs; b) Productivity through compounding; c) Mechanisms that specify relations between signs in sentences, particularly to a visual gestural language (i.e., the establishment of loci in signing space); d) The possibility of simultaneous signing. These are all aspects entirely distinctive to a language in a different mode. We also propose experiments in linguistic processing of signs by the deaf.